The invention relates to a combustion engine of turbocompound type and, more particularly, to such an engine incorporating an exhaust gas brake preamble to patent claim 1.
A known means of improving the braking effect of a four-stroke combustion engine is to arrange an exhaust gas brake damper in the exhaust gas manifold outlet. Closing this exhaust gas damper will cause the engine to pump out exhaust gases during the exhaust stroke against the closed damper, thereby resulting in increased engine brake effect. In order inter alia to achieve a quicker brake effect response, endeavours have been made to place an exhaust gas brake damper as close as possible to the cylinder exhaust gas valves, preferably directly after the point where the cylinderwise exhaust gas branch ducts merge to form a common exhaust gas duct. In certain cases the damper may also be placed directly after a turbocharger where two or more separate exhaust gas manifolds lead exhaust gases to a turbine with two or more guiderails in the turbine, with the object of reducing pulsating noise on the exhaust gas side of the engine.
In connection with turbocompound engines, a number of solutions intended to increase the braking effect in turbocompound engines have been patented. For example, EP,B,272680 and U.S. Pat. No. 4,748,812 refer to solutions for engines with so-called Jake brakes. Such a brake provides engine braking by brief opening of exhaust gas valves at the end of the compression stroke. The known solutions mentioned use a special exhaust gas damper which is arranged between the supercharger turbine and the power turbine and closes the flow from the supercharger turbine at the same time as a throttled duct opens so that the power turbine can pump exhaust gases against a throttle at the same time as the power turbine transmission is reversed. This solution becomes technically complicated and expensive, involving a reversible gearbox with several gears. U.S. Pat. No. 5,119,633 refers to an alternative for engines with so-called Jake brakes whereby a simple bypass of the power turbine is activated as soon as engine braking is activated. Increased braking effect is thereby intended to be achieved by the power turbine driving power supplied to the crankshaft being largely disconnected because the flow through the power turbine ceases.